(1) Field of the Invention
The present invention relates generally to a fiber optic sensors and more particularly to a fiber optic accelerometer.
(2) Description of the Prior Art
Linear fiber optic arrays are used in Navy tactical and surveillance towed array applications as well as commercial towed seismic streamer applications for oil and gas exploration. Linear arrays may also be used in ocean bottom applications or placed down oil wells for oil field monitoring.
Fiber optic sensor arrays use interferometers and lasers to interrogate a plurality of sensors formed in an optical fiber. Typically these sensors are made from a fiber optic sensing segment positioned between two reflective portions. The sensing segment is usually wound on a compliant mandrel. Acoustic pressure on the sensor results in strain in the fiber optic sensing segment. Strain in the fiber optic sensing segment is measured using the interferometer. Various schemes such as wavelength division multiplexing and time division multiplexing exist for increasing the number of sensors on a single optical fiber. Fiber optic sensor arrays are also known that use multiplexed fiber laser sensors to provide an acoustic pressure signal.
A newer type of electronic linear sonar array is a vector sensor array. A vector sensor array uses sensor elements that provide a vector reading of the acoustic field, rather than just the scalar pressure. A typical form of the sensor element involves a combination of 2 or 3 orthogonal accelerometers and a pressure sensor.
Such a vector sensor array has several potential advantages over linear arrays of pressure sensors. Because of the added directionality of the individual element, the gain is increased per unit array length. A single linear array can resolve the left-right bearing ambiguity seen in pressure sensor arrays. Finally, the array can increase effective gain against anisotropic background noise fields. Previous linear vector sensor arrays have used conventional (non-fiber optic) accelerometers and pressure sensors combined with electronic telemetry. They have shared the same intensive, complicated hand assembly techniques that have resulted in high cost and low reliability in pressure sensor arrays.
It is therefore the intent of this invention to provide a directional fiber optic accelerometer that can be used to form a linear array of vector sensors.